The present invention relates generally to shielding cylinders for electrical machines and more specifically relates to a shielding cylinder for an electrical machine having a superconductive excitation winding and a method for manufacture of the cylinder.
A turbogenerator having a superconductive excitation winding is disclosed and illustrated in longitudinal cross section in the article "Turbogeneratoren mit supraleitender Erregerwicklung" in Bull. SEV 64 (1973), 17, 18 August, pages 1040 to 1050 (see especially page 1043, FIG. 3). The excitation winding is cooled by liquid helium. A cold rotor body, which supports the excitation winding, is arranged within an outer, warm cylinder, with a high vacuum generated in the interspace between the cylinders. Fastening of the inner rotor body and a transfer of torque to the shaft ends (which are at room temperature) is accomplished by thin fittings which are cooled with helium. In the interspace between the cylinders under vacuum, a thin cylinder, a "Strahlungszylinder" is provided which acts as an additional electrothermal shield. The thin cylinder absorbs the heat radiated by the outer cylinder and reduces a residual amount of the magnetic fields which permeate the outer damping cylinder to a magnitude which can be tolerated by the superconductor. The manufacture of such shielding cylinder is rather complicated, however, in view of the large dimensions of such cylinder. The cylinder may have a length amounting for example to 10 meters.
It is a primary object of the present invention to provide a shielding cylinder for an electrical machine with superconductive excitation winding which cylinder has very precise circular and cylindrical dimensions. If the dimensions are not precise, the danger of a breakdown otherwise exists.
It is a further object of the present invention to provide a method of simple construction of the cylinder.
It is an advantage of the present invention to permit a precise working and machining of the shielding cylinder during manufacture. In this way, correct and proper dimensions of the cylinder may be ensured.
Advantageous further developments of the present invention include a simple and economical manufacture of the cooling ducts. An arrangement of annular ducts serves as collecting ducts. The annular ducts are arranged within portions of the outer surface of the inner cylinder as well as within a corresponding section of the inner surface of the outer cylinder. Such an arrangement results in a sufficiently large cross section for these ducts. One or more bulges may form annular ducts and will serve at the same time as mechanical reinforcements of the shielding cylinder. The bulges can also serve as the annular collecting ducts.
The shielding cylinder is manufactured most advantageously by placing a heated inner cylindrical member upon a mandrel. A mechanical treatment which then follows ensures the proper and correct dimensions of the inner cylinder, with axial and annular ducts being arranged in the shielding cylinder in a simple manner. An outer cylindrical member is heated and then pushed onto the inner cylinder. Machining of the outer cylindrical member then follows and gives the shielding cylinder its final shape.
A two piece mandrel makes possible a simple method of manufacture, even for very long and thin shielding cylinders.